If you include cycling as part of your exercise program, you’ve probably experienced both aerobic and anaerobic exercise. The aerobic component comes into play when you’re riding along a flat stretch of road, breathing hard but still able to carry on a conversation. The anaerobic action kicks in when you start climbing a hill and find that you have to pump your legs very hard and breathe heavily. Your heart is beating at up to 80 percent of its maximum rate at the aerobic level and from 80 to 100 percent when you’re climbing that hill.
In aerobic exercise, your muscles use oxygen to help them burn glucose and fatty acids to produce the adenosine triphosphate, or ATP, muscles need to contract. Aerobic exercise is any activity -- such as walking, jogging or cycling -- in which your heart rate and breathing are elevated but you’re able to sustain the effort. Aerobic exercise is also known as cardiovascular exercise, and it helps strengthen your heart and circulatory system.
In anaerobic exercise, your muscles use creatine phosphate for energy. That supply runs out in about 30 seconds, however, so the muscles start producing ATP from glycogen, formed from glucose, without using oxygen. Simply put, the muscles are working so hard during these intense bursts of power that they don’t have time to wait for oxygen to burn fatty acids or glucose, so they burn glycogen. This type of energy supply produces lactic acid, which makes your muscles sting and forces you to stop exercising.
Calculating Heart Rate
Aerobic and anaerobic levels of exercise are often determined by your heart rate during exercise and are expressed as a percentage of your maximum heart rate. The best way to calculate your precise MHR is by doing an electrocardiogram treadmill test in a doctor’s office. A commonly accepted estimate would be your age subtracted from 220. For instance, a 50-year-old woman’s maximum heart rate would be 170 beats per minute. While exercising on a bike, the best way to measure your heart rate is with a monitor strapped to your chest that transmits a measurement to a wrist receiver.
The aerobic exercise zone is anything between 50 percent and 80 percent of your maximum heart rate. You should exercise at between 50 to 60 percent of your MHR while warming up and cooling down. At 60 to 70 percent of your MHR, you should be able to talk comfortably and to ride for an extended period, burning glucose and then fat for energy. The highest aerobic zone is 70 to 80 percent of your MHR, and at this level you are cycling hard or climbing a hill. Cycling coach James Herrera recommends spending 25 to 50 percent of your total riding time at this higher aerobic training level but not on back-to-back training days.
Your body will begin working anaerobically when you exceed 80 percent of your MHR. You will start gasping for air and lactic acid will start building up in your muscles. You can only go so long before you have to decrease your effort level. But by doing a series of short, high-intensity bouts of anaerobic training, such as hill repeats on your bike or high-cadence sprints on a stationary bike, you will improve your ability to burn oxygen at higher heart rates.
Examples of Anaerobic Workouts
Chris Carmichael, cyclist Lance Armstrong’s former coach, recommends a variety of interval training workouts – from six-minute, steady-state sessions at 92 to 97 percent of your MHR followed by six minutes of recovery cycling to 60-second power intervals followed by 90-second recoveries of easy cycling. The number of intervals you do depends on your fitness level, but you can slowly increase the number of intervals or the length of your intervals as you improve over the coming weeks.
Jim Sloan is a writer and editor in Reno, Nevada. He has been a journalist for more than 25 years and is the author of two books, "Staying Fit After Fifty," and "Nevada: True Tales from the Neon Wilderness."